1. Field of the Invention
The present invention relates to a headrest attached to a seat back of a vehicle seat, and more particularly to a headrest mounted on a seat back for the front passenger seat or rear seat.
2. Description of the Related Art
A headrest will be comfortable if the angle of forward inclination thereof can be finely adjusted to match the passenger's physique or the like. It is also convenient if the sides of the passenger's head are supported together with the back of the head in cases such as when the seat is reclined. Furthermore, if the headrest can be moved forward and rearward, it will be even easier to adjust to the passenger's physique or the like. In addition, for a front passenger seat or a rear seat, when there is no passenger sitting therein, the driver's field of view being blocked can be prevented if the headrest is folded up or retracted. Such a configuration is disclosed in, for example, Japanese Utility Mode Application Laid-Open (Kokai) No. 5-048750; however, the headrest disclosed in this publication is very complex in structure and high in cost. In the headrest disclosed in Japanese Patent Application Laid-Open (Kokai) 2006-264431, the headrest can be moved or tilted using an electric motor; however, the structure of this headrest also requires many numbers of members and parts, and the headrest is expensive.
In a construction in which a headrest is made to move or tilt, in the interest of safety, it is necessary to make provision so that it does not move when a rearward or quartering rearward force is applied. For this purpose, in Japanese Utility Mode Application Laid-Open (Kokai) No. 5-048750, a ratchet mechanism having engagement teeth is used. However, in this structure, a manipulation, using a manipulating member, is required to engage or disengage a latching body for latching the engagement teeth, and the latching position is limited to the position of the tooth surfaces of the engagement teeth (stepwise); as a result, stepless-fashion fine adjustments cannot be made, which is a drawback.
In general, when a coil spring having an inner diameter smaller than the diameter of a shaft is wound about this shaft, the properties are such that, if the shaft or the coil spring is turned in a direction in which the coil spring tightens, the coil spring tightens down on the shaft and turning is restricted (or movement is very heavy), whereas, if, on the other hand, the shaft or coil spring is turned in the opposite direction, then the coil spring will turn freely (or very lightly), sliding over the shaft. For convenience, this structure is, hereinafter, called a coil spring type torque limiter. This coil spring type torque limiter has advantages in that the structure is simple and inexpensive, and in that, merely by turning the coil spring in the loosening direction, the initial position (phase) can be adjusted in a stepless manner.